Using a long incubation period rabies model in mice, attempts will be made to determine the limits of interruption of the movement of virus towards the central nervous system using physiological and immunological methods. Using a second virus model which causes inapparent or abortive CNS infection in mice, the sequential histopathology occurring in the brain will be described. The behavioral changes resulting from such infection will be examined using psychophysiological tests. The long incubation period model will permit a study of the immunological response of the host to vaccines and sera of different types and to different regimens. Methods of presymptomatic rabies diagnosis will be explored and their limits determined.